JPH0690085B2 - Interference filter spectroscope - Google Patents

Description

The present invention relates to an interference filter spectroscope for rotatably disposing a bandpass interference filter in a parallel optical path and selecting monochromatic light.

Prisms and gratings are used to extract monochromatic light from various light sources. This method is difficult to adjust the optical axis and is expensive. In a system that obtains monochromatic light of a predetermined wavelength by rotating an existing interference filter in a parallel optical path, the transmittance decreases as the incident angle increases, and the tip is divided into two. The present invention employs an interference filter capable of obtaining steep and undistorted monochromatic light over a wide range, and attempts to obtain desired monochromatic light by setting the incident angle.

As shown in Table (1), on the glass substrate G heated to 300 ° C, titanium dioxide with a refractive index of 2.25 was added to the optical film thickness (n × d)
Is vacuum-deposited as a 217.2 nm thin film, and the refractive index is
1.38 magnesium fluoride of 1.38 is similarly deposited as a thin film of the same optical thickness. The optical film thickness is 1/4 of the wavelength of transmitted light. This dielectric thin film consisting of titanium dioxide and magnesium fluoride is alternately repeated to form 11 layers. The cavity layer, which has the 12th intermediate biofilm sequence, has a refractive index of 2.25 and 1.
Cerium fluoride (refractive index: 1.58), which takes the interval 38, is deposited as a thin film with an optical film thickness of 435 nm. The optical thickness of the cavity layer is an integral multiple of 1/2 of the transmission wavelength. Titanium dioxide and magnesium fluoride are alternately and repeatedly laminated on the cavity layer to form a total of 23 dielectric thin films. The upper and lower repeating layers are symmetrical with respect to the intermediate cavity layer.

FIG. 2 shows the result of measuring this dielectric multilayer film with a spectroscope while tilting it one by one with respect to the incident light beam as shown in FIG. Incident angle (θ °) is 0,15.27,21.75,26.85,31.25,3
The transmission spectrum curves when changing to 5.25, 38.97, 42.53, 45.95 are arranged in order from the right side. It is possible to obtain monochromatic light that is steep and has an extremely small half-width over a wide range of incident angles. In a conventional filter that employs a dielectric material having the same refractive index as that of the alternating layers in the cavity layer, the transmittance decreases and the tip is divided into two as the incident angle increases. Since a dielectric material with a refractive index between those of the refractive indexes is adopted, there is no deviation in the transmission wavelength values for the S and P waves, which are the polarization components of the incident light, and a stable transmitted light spectrum with no attenuation or tip distortion is obtained. can get.

FIG. 3 is a plot of the spectral data when the interference filter 1 is tilted in the parallel optical path. Incident angle (θ °)
Shift of peak transmission wavelength (monochromatic light wavelength) with respect to
The relationship of λ) is shown. From the relationship or the like between the optical thickness and transmission wavelength Apart from this data, the incident angle transmission wavelength lambda _0, A is an interference filter specific constant when the θ = 0 ° θ
The transmission wavelength λ at the time of is calculated from the equation.

λ = λ ₀ × (1-A × Sin ² θ) ^1/2・ ・ ・ When the constant A was obtained and plotted in Fig. 3, the two coincided as if the X mark was connected. This is due to the adoption of the present interference filter that produces monochromatic light with a very small full width at half maximum without the tip distortion as shown in FIG.

FIG. 1 shows an embodiment in which a predetermined transmitted monochromatic light is obtained from a light source 2, and an interference filter 1 is rotatably arranged in a parallel optical path from a fiber collimator 3. A knob 4 and a gear are attached to a support shaft 5 of the interference filter 1, and a gear meshing with the gear is provided on the variable resistor 6 side. The output of the variable resistor 6 which is a potentiometer is digitally converted and connected to the computer 7. The computer 7 first obtains the incident angle (θ) by the input from the variable resistor 6 and calculates the wavelength (λ) of the transmitted light by the above theoretical formula, and displays the result on the display. In the figure, 850 nm transmitted monochromatic light is obtained. A pulse motor may be adopted instead of the knob 4, and may be provided so as to sequentially transmit wavelengths at a constant interval. Further, alumina, silicon monoxide, zirconium dioxide may be used as the cavity layer (resonance layer) of the interference filter 1, and silicon dioxide or the like may be used as the dielectric thin films that are alternately laminated.

Next, the operation will be described. The knob 4 is turned to set the interference filter 1 in the parallel optical path at a predetermined angle. This angle is detected by the variable resistor 6 and input to the computer 7 to calculate and display the peak wavelength of the transmitted monochromatic light (first
Figure).

An embodiment as a spectrophotometer is shown in FIG. Standard light source 8
The LED light source 9 is selectively made incident on the interference filter 1, and the transmitted light is guided to the light receiver 10. A spectral distribution is created from the detected tilt angle of the interference filter 1 and the luminous intensity information.
First, the standard light source 8 is spectrally separated, and the luminous intensity at each wavelength is stored. Next, the LED light source 9 is dispersed by the same operation to obtain the luminous intensity at the wavelength, and the division is performed to calculate the luminous intensity at each wavelength.

In short, according to the present invention, dielectric thin films having different refractive indexes are alternately and repeatedly laminated, and dielectric thin films having a refractive index between those of both dielectric thin films are laminated on the dielectric thin films to form a cavity layer, An interference filter in which dielectric thin films having different refractive indexes are repeatedly laminated on the cavity layer in the same manner, and means for changing the incident angle by rotatably arranging the interference filter in a parallel optical path. Since there is a means for calculating the transmission wavelength from this incident angle, it is possible to select transmitted monochromatic light that is steep and has little distortion by setting the incident angle of the interference filter.

[Brief description of drawings]

The drawings show one example of the present invention, FIG. 1 is a schematic explanatory view, FIG. 2 is a transmission spectrum diagram when the incident angle of an interference filter arranged in a parallel optical path is sequentially changed, Fig. 3 is a graph of the measured and theoretical values of the peak transmission wavelength when the interference filter is gradually tilted, Fig. 4 is an explanatory view of the refraction of light in the interference filter, and Fig. 5 is an implementation block as a spectrophotometer. It is a figure.

Claims (2)

[Claims] 1. A dielectric thin film having a different refractive index is alternately and repeatedly laminated, and a dielectric thin film having a refractive index between those of the two dielectric thin films is laminated thereon to form a cavity layer, An interference filter in which dielectric thin films having different refractive indexes are repeatedly laminated on the cavity layer in the same manner, and means for changing the incident angle by rotatably arranging the interference filter in a parallel optical path. , An interference filter spectroscopic device having means for calculating a transmission wavelength from this incident angle. 2. Adopting two from the group of titanium dioxide, magnesium fluoride, and silicon dioxide as the dielectric thin film to be laminated alternately, as a cavity layer having an optical thickness of an integral multiple of half the transmission wavelength, The interference filter spectroscopic device according to claim 1, wherein one is selected from the group consisting of cerium oxide, alumina, silicon monoxide, and zircon dioxide.